The present invention relates generally to the design and construction of precast segmental viaducts, and more particularly, to the erection and assembly systems and equipment of bridge segments during the construction of the viaducts of spans of up to 60M, with continuous or simple supported spans, with straight or moderately curved alignments. Precast segmental viaducts are commonly built using the following three methods:
The first method is the Span-by-Span Construction method illustrated in FIGS. 1-6. According to this technique, precast concrete segments 10 having match-cast joints, are assembled end to end along one span of the viaduct over two consecutive piers A, B and B, C, and are placed temporarily on steel trusses 11 and 12 that are supported by steel brackets 13 fixed on the piers.
Once the segments are adjusted over the trusses, post-tensioned cables are inserted into the segments and stressed. The span is then self-supported. Trusses are lowered and launched to the next span and the same construction cycle takes place again. Segments are transported either using the already built viaduct, or from the roads underneath the viaduct in construction. Cranes 17 (FIG. 1) 18 (FIG. 5) or gantries are used for the erection of segments, working at ground level, or over the already built span. The trusses are generally twin parallel trusses that extend between piers and on both sides of the span. The pier brackets are bolted to the piers or the loads are transferred directly to the pier footings. This method was applied exclusively for simple supported spans of straight viaducts for spans not exceeding 40M (120 FT). The segments are usually single box girders with wings on both sides and the trusses are placed under such wings. FIG. 3 illustrates boxguiders 14 supported on a pair of steel beams 15 and 16. These conditions considerably reduce the area of application of this method. For the safety of people and vehicles moving close to the construction area, a system relying on temporary supports is not recommended.
The second method is the Progressive Placing Construction method illustrated in FIG. 5, 7a, b and c. When spans are larger than 40M (120 FT) and/or the viaducts are curved, and/or the box girders have reduced wings, the Span-by-Span method is not usually applicable. In these cases, the progressive placing construction has been used in precast segmental viaduct construction. According to this method, the segments are placed and assembled one by one, from one end of the viaduct to the other, in cantilever construction, self-supported. The segments are usually transported using the viaduct being constructed. A swivel crane 19 placed over the last segment assembled takes the new segment from behind and places it in front. Cantilever type cables are then inserted and stressed. The swivel crane is moved to the top of the newly assembled segment and the cycle repeats itself until the cantilever reaches either the next pier, which may be the actual pier, or a temporary pier. This method allows to span up to 70M (210 FT) and can be used in curved viaducts with continuous spans, but has some disadvantages. In particular, it requires the swivel crane to be moved after erection of each segment; it cannot be applied when the viaduct is too narrow; it is very slow; and it requires additional post-tensioning.
The third method is the Balanced Cantilever method of construction illustrated in FIG. 8 which is usually used for viaducts with spans from 70M (210 FT) to 150M (450 FT). It was previously used with cast-in-situ segments and is now more commonly applied on precast segmental viaducts of large spans. As illustrated FIG. 8 the principle of this method that can be used on viaducts with curved alignments and different types and shapes of box girders an overhead gentry 20 supported on a pier is used to move the segments from the completed section to build out from each pier.
The prior art methods suffer from different disadvantages. The Span-by-Span construction requires that trusses be supported by pier brackets outside the pier which are difficult to install and remove, and as previously noted, can interfere with traffic clearances and security. Furthermore, it requires the movement of cranes at ground level and has limitations concerning curvature of viaducts, is not applicable for continuous structures, wide single box girders, bridge deck sections U shaped, or generally, girders without wings.
The trusses used in prior art methods cannot take any torsional moments as they are simply placed over the pier brackets. In general, in the Span-by-Span method and the Progressive Placing method, the gantries or cranes are to be moved, independently of the trusses or other temporary supports, after assembly of each segment, which is a critical operation in the path of construction. In view of the foregoing, there is an evident need for an improved viaduct construction system that overcomes the deficiencies of prior art methods.
More particularly there is needed a construction method for precast segmental, match-cast joints, that is fast, structurally stable, does not require temporary supports, pier brackets or trusses that can interfere with vehicle traffic underneath the viaduct being built. A method that can accept curved alignments, be self-launched with integrated erection and assembly equipment, and that can be used with different widths of segments, multibox sections, or U shaped sections allowing the construction by either simple supported span-by-span or with the continuity of the structure over the piers.